Crimped textile filament



April 1960 A. L. BREEN 2,931,091

CRIMPED TEXTILE FILAMENT Filed Feb. 26, 1954 2 Sheets-Sheet 1 INVENTORJlZvirzLhBreeJz ATTORNEY April 1960 A. L. BREEN 2,931,091

CRIMPED TEXTILE FILAMENT Filed Feb. 26, 1954 2 Sheets-Sheet 2 INVENTOR"filvirz LBren/ BY UDfi W ATTORNEY United tates CRIMPED TEXTILE FILAMENT Application February 26, 1954, Serial No. 412,781 9 Claims. (Cl. 2882)This invention relates to synthetic textile fibers and particularlytextile fibers possessing a permanent crimp.

Various methods have been proposed and used to produce crimped syntheticfilaments. The principles of these crimping methods comprise mechanicaltreatment of the filaments spun in normal fashion as well as applicationof specific conditions of spinning or aftertreating which bring aboutdifierential physical properties over the cross-section of the singlefilaments.

Newer proposals of producing an improved crimp in synthetic fiberscomprise the spinning of two or more dilferent materials together sothat they form a unitary filament which contains the components in aneccentric relation over the cross-section of the filaments. When, forinstance, two materials are used together which possess substantiallydifierent physical properties, for example, different residualshrinkage, a crimp is brought about by the application of a suitableafter-treatment to the spun and drawn composite filaments. These crimpedfilaments may be quite satisfactory as long as only relatively smalltensions are applied during their use. However, with the application ofhigher tensions, the crimped filaments of the prior art do not possessthe optimum properties and the highest possible crimp retention. Perhapsthis is the reason that none of these composite crimped filaments havebeen commercially produced and used.

It is, therefore, an object of the present invention to provide crimpedtwoor multi-component composite filaments which have improved recoveryproperties and higher crimp retention. It is another object of theinvention to produce crimped filaments with improved mechanicalproperties. It is another object to produce crimped filaments having onapplication of high tensions, as they occur in practical manufacture offabrics therefrom, a considerably higher crimp retention than heretofore obtainable. Further objects will appear as the description of theinvention proceeds.

The term tensile recovery is well known (cf. US. 2,604,689, Beste andHoffman, Textile Research Journal, vol. 20, No. 7, July 1950, page 441,and also Texile Fiber Yarns and Fabrics, by E. R. Kaswell, published byRheinhold Publishing Corporation in New York City, l953).and is definedas the extent to which a yarn recovers its original length after beingstretched, a stressstrain curve being used to determine tensile recoveryunder the testing conditions. The determination is usually carried outat a constant rate of elongation. For example, a given sample of yarnmay be elongated at a rate of 1% per minute, held 30 seconds at the 5%elongation and then allowed to recover at the same rate which it wasextended and the recovered length measured. The tensile recovery (inthis instance for 5% elongation) elongation recovered total elongationatent the tensile recovery values are given for a stated totalelongation. v

The objects of this invention are effected by producing a crimpedcomposite filament, in which the component having the higher tensilerecovery properties is the component subjected to the higher strain onstraightening the crimp by an external force. This component will becalled the load bearing component in the following description of theinvention. The new improved crimped filaments of this invention may beobtained by different methods. One method comprises spinning togethertwo or more synthetic polymeric fiber-forming materials, of which thematerial having the higher shrinkage after drawing has the lower tensilerecovery properties, in such a way that the materials form over thecross-section of the single composite filament two or more distinctzones which extend through the entire length of the filament ineccentric fashion, whereby only one, or part of, or all the componentstake part in forming the surface of the single composite filament,stretching the composite filament, length stabilizing the component orcomponents with the higher shrinkage by the application of heat or othermeans to the drawn composite filament while it is kept under tension,which results in crystallization of this polymer without affecting theother compo nent or components substantially, and subjecting the thustreated composite filaments in a substantially tensionless state to ashrinking treatment.

An important characterizing feature of this method of the presentinvention is the discovery that in composite synthetic crimped filamentswherein the load bearing component has the lower tensile recoveryproperties, the overall properties and particularly the crimp retentionof the filaments can be greatly improved by subjecting the drawncomposite filaments prior to the development of crimp to a treatmentwhich results in crystallization and length stabilization of thenormally load bearing component and which does not afiect or onlyslightly affects the other component. Any treatment which meets theserequirements may be used. Such treatments are, for instance, a taut heattreatment at a temperature high enough and for a time long enough toprovide crystallization of the desired polymeric component. Thetemperatures applied in this heat treatment will generally be higherthan the apparent minimum crystallization temperature (T of thecomponent which is to be length stabilized. The apparent minimumcrystallization temperature (T is defined as the lowest temperature atwhich a marked rate of density change, which is known to occursimultaneously with crystallization, takes place within six hours. Inother instances, crystallization and length stabilization can preferablybe brought about by a treatment of the taut composite fiber with certainpolar organic liquids which are latent solvents for the amorphousregions of the component to be stabilized.

In the spinning, the polymers are not appreciably blended together inthe melt but are fed separately to a shaped orifice where they aresimultaneously extruded. The orifice is, then, adapted to receive thecomponents separately for simultaneous extrusion to form a filament inwhich each component is substantially localized but is held to the othercomponent in an eccentric relation. The extrusion can be such that thecomponents are localized and held together in a side-by-side. structurein which both components form part of the surface of the composite. Theextrusion may also be such that one component forms a core and the othera sheath to form a. composite referred to hereinafter as a sheath-corestructure. In this structure only the sheath contributes to the surfaceof the composite. With the spinnerets described herein, melt spinningleads to composites which are generally smooth and have cross-sectionswhich are substantially round with boundary lines that are regular.

The composite filaments are stretched and the resultant Stretchedfilaments are subjected to the length stabilizing treatment and afterthat treatment they are given a shinkingtreatment while they are in afree-t'o-shrink state. The crimp in the new crimped filaments of thisinvention is brought about not only by a difierential in shrinkage inthe components of the composite but by positioning the components inrespect to helical crimps so that the component with the better tensilerecovery properties is the load-bearing component.

In the figures:

Figure 1 is a plan view of the spinneret assembly shown in Figure 2;

Figure 2, taken on line 22 of Figure 1, is a crosssection of a spinneretof this invention showing the routes of polymer in the formation ofsheath-core structures;

Figure 3 is taken on line 3-3 of Figure 2;

Figure 4 is taken on line 44 of Figure 2;

Figure 5 is a cut taken on line 5- 5 of Figure 2;

Figure 6 is a cross-section of a spinneret of this invention showing theflow of polymer in the formation of side-by-side structures;

Figure 7 is taken on line 7-7 of Figure 6;

Figure 8 shows cross-sections of the sheath-core filaments of thisinvention; and

Figure 9 shows cross-sections of the side-by-side filaments of thisinvention.

Figure 10 is a sectional perspective of a fragment of a composite in acrimp form referred to as alpha crimp;

Fig. 11 is a sectional perspective of a fragment of a composite in acrimp form referred to as beta crimp; and

Figure 12 is a diagram of apparatus which can be used in applying aprocess of this invention in a continuous manner.

Referring first to Figure 2 it can be seen that the top component orfilter pack 1 of the spinneret has two chambers 2 and 3. Each is fed adifferent polymer. The chambers are separated by wall '4 and in thebottom of the top portion are a plurality of holes 5 cooperating withoutlets below. The chamber 3 and the holes '5 therein cooperate with thegrooves or recesses 6 and 23 in the center portion of adapter 7 and feedthe polymer melt to the vertical holes '8 or tubes 31. These tubes 31extend downwardly into the orifices 9 contained in the bottom portion orspinneret face 10. The chamber 2 permits the feeding of polymerdownwardly through holes 5 which cooperate with holes 11 in centerportion 7 to permit the flow of polymer to grooves or recesses 12 and 29in the bottom portion 10. The plan views of the top, center and bottomportions may be seen in Figures 1, 3 and 4, respectively. As shown,gaskets 25 are provided for sealing purposes, the assembly being heldtogether by means of bolts or by pressure.

As shown in Figure 2 and in an enlarged manner in Figure 5, polymer 13coming to the holes 8 or tubes 31 from the chamber 3 constitutes thecore feed. As this polymer leaves tube '31 which is surrounded by themelt 14 of polymer coming from chamber 2 and constituting the sheath,bonding occurs so that in the tapered section 30 of orifice '9, polymers13 and 1 1 are being extruded simultaneously with polymer 14 completelysurrounding the polymer-13. It is to be noted that tube31 iseccentrically located in the orifice 9. This is done purposely to getthe eccentric relation of the polymers, for the more pronounced theeccentricity, the better are the crimp results. As can be seen in Figure8, the filaments thus produced by melt spinning have substantiallyround, smooth surfaces. Even the core is substantially round and smoothand in all cases the .core does not break through the surface. That is,even in such a filament as 15 there is polymer 14 surrounding the coreeven though the core comes very close to the outer edge atone place.

In the production of eccentric composite filaments such as sheath-corestructures, one uses a material 13 and a material 14 which are sorelated that material 13 has the better tensile recovery properties. Ifmaterial 14 has a higher shrinkage than material 13, the crimpedstructure shown in Figure 10 wherein the material 14 is located on theinside of the helical coil is obtained. This type of crimp in which thematerial 14 having the lower tensile recovery properties is located onthe inside of the coil is referred to herein as alpha crimp. Since thematerial on the inside of the helical coil is the load-bearingconstituent of the composite, it is desired to have that material be thematerial having the better recovery properties. By the process of thisinvention, it is possible to produce such crimped filaments as are shownin Figure 11. In this figure, material 13 is on the inside of thehelical coil and has the better tensile recovery properties. This typeof crimp shown in Figure 11 is referred to herein as beta crimp." Asmentioned above, one method of this invention for producing the desiredbeta crimp involves the conversion of the alpha crimp type to the betacrimp type. This is referred to herein as reverse crimp; in thisreversal the material 13 has been converted so that it is now thematerial having the higher shrinkage while retaining its better tensilerecovery properties. As will appear hereinafter, it is also possible bythe selection of polymeric materials, heretofore not used, to producethe desired beta crimp without applying the length stabilizing stepdescribed above to reverse the alpha crimp.

A relatively low tension applied to the crimped filament results inextension of the coils and finally in straightening of the coils becauseof the very low crimp modulus. Tensions which are higher than the crimpmodulus will extend the straightened composite filament whereby theshorter component which forms the inside of the coil bears a relativelygreater part of the total load applied. It follows therefrom that arelatively higher strain is applied to the load-bearing component thanto the coacting component in a tensioned crimped composite filament.When the load-bearing component has the lower tensile recoveryproperties, which is the case with the combinations of synthetic highpolymers proposed herebefore for the preparation of crimped compositefilaments, the degree and tightness of the crimp will be reduced afterapplication of relatively high loads, because the load-bearing componentdoes not recover as much as its counterpart. The new composite crimpedfilaments of this invention do not have this disadvantage because thematerial with the better tensile recovery properties has been made to bethe load-bearing component.

It is evident from the foregoing that it is of great importance forevaluating crimped composite filaments to have a reliable method formeasuring the crimp retention. A commonly used method is described egg.in US. 2,287,099. In this test, relatively low loads, equivalent to 0.03g./denier are applied to the crimped filaments while immersing them for30 seconds into water of 60 C. These tensions are much lower than thestrain usually imposed on the single filaments in normal use of textileproducts containing these filaments. Therefore, a more stringent testhas been developed, which simulates more the actual conditionsencountered in practical use of the crimped filaments.

The crimped yarn or filaments are formed into a skein the length ofwhich is measured without applying any tension (a, in centimeters). Theskein is then loaded with a Weight corresponding to 0.01 g./denier andthe straightened length of the skein is measured (12, in centimeters).The skein is then loaded for 30 seconds with a weight corresponding to1.0 g./ denier. The filaments are allowed to recover, after removal ofthe load, for 30 seconds and the length of the skein is again measured(c, in centimeters);

(igmT) In the examples parts and percentages are by weight.

Percent crimp permanence 100 Example I Poly(ethylene terephthalate)flakes having an intrinsic viscosity of 0.67 in a solvent mixture of58.8 parts by weight phenol and 41.2% by weight of trichlorophenol andpoly(hexamethylene 'adiparnide) flake having an intrinsic viscosity of1.02 in m-cresol are melted sep arately and extruded at 285 C. through amulti-hole spinneret assembly shown in Figure 2. The extruded filamentis air quenched. The polyester melt is extruded through the inner tubeof the spinneret and the polyarnide through the outer space surroundingthe tubes, thus forming a sheath-core filament. Figure 8 shows across-section of a bundle of the eccentric sheath-core filaments thusobtained. This drawing, based on a microphotograph, shows clearly theeccentric position of the polyester cores in the polyamide sheaths overthe crosssection of the single filaments forming the fiber bundle.

The eccentric sheath-core filaments are attenuated by pulling them asthey are spun away from the spinneret holes with a speed which is about100 times as high as the speed of the extruded melt. After spinning andcooling, they are drawn over a pin at room temperature (20 C.) to 3.3times their original length. About 100 yards of the stretched filamentswere tightly wound on a bobbin, and the bobbin was heated for 30 minutesin an electric oven, the temperature of which was 115 C. The cooledfilaments were then unwound from the bobbin and showed upon inspectionno distinct crimp. However, they possess a potential crimp which can bedeveloped immediately after the heat treatment or at any time after thefiber is processed into woven textile materials or into knitted goods orafter cutting the fibers into staple lengths.

Example II A part of the continuous filament of. Example I containingthe potential crimp was skeined and hung in boiling water for one minutewithout applying any tension to the filaments. A very tight helicalcrimp developed instantly. The filaments contained on an average 50crimps per inch. Microscopic inspection of the filaments showed that thecore of poly(ethylene terephthalate) was positioned in the outer portionof the single coil and the thicker parts of the polyamide skin weresituated on the inside of the single coil. Therefore, the filamentscontained the beta crimp.

Example III Part of the eccentric sheath-core composite filament yarn ofExample I was plyed and twisted to a yarn containing 56 filaments with atotal denier of 180. The twist was 0.5 turn per inch. This yarn was knitinto tubing which when flattened to double thickness measured 3%" wide.A piece of this tubing 12 inches long was placed in boiling watercontaining 0.5% Duponol for 30 seconds. The fabric was then rinsed,centrifuged and dried in the open air. The dry fabric was found tomeasure 3 /8" wide and 5%" long. The bulk and covering power of thefabric were correspondingly increased. Moderate tension causedstretching of the fabric beyond the original dimensions but the shrunkenform returned almost completely upon release of such tensions. This goodshape retention of the boiled-off knit fabric is attributed to the goodcrimp retention of the crimped fibers composing the fabric.

If the spun and drawn filaments of Example I are given the shrinkagetreatment of Examples H or III without applying first the lengthstabilization treatment of Example I, highly crimped filaments areobtained. However, microscopic inspection of the cross-section of thesecrimped filaments shows that the cores consisting of the polyester arepositioned on the inner portion of the coils and the thicker portions ofthe polyamide skin are on the outside of the coils. These fiberstherefore possess the alpha crimp and do not possess the crimp retentionof the beta type of this invention.

Example IV Poly(ethylene terephthalate) flakes having an intrinsicviscosity of 0.67 in a solvent mixture comprising 58.8 parts by weightphenol and 41.2 parts by weight trichlorophenol and polyethylene, havingan inherent viscosity (0.5% concentration) of 0.88 in tetralin measuredat C., were melted separately and extruded at 296 C. through a spinneretas shown in Figure 2. The polyethylene melt was extruded through theinner tube of the spinneret and the polyester through the outer spacesurrounding the tubes, thus forming a sheath-core filament.

After spinning and winding, the quenched sheath-core filaments werepassed through a water bath at 30 C. to a roll heated to 65 C. and thento an unheated roll rotating at a higher speed whereby the yarn wasstretched 2.6 times its original length.

A part of this continuous filament yarn was skeined and hung in boilingwater for 1 minute without applying any tension to the filaments,whereupon the yarn crimped spontaneously. Microscopic examination of thecrimped filaments showed that the heavy part of the polyester skin wassituated on the inside of the single filament coil, which corresponds tothe alpha crimp described above. These alpha crimped filaments showed acrimp retentivity of less than 25% when measured according to the newmethod described above.

Another portion of the freshly spun yarn was wound tightly on a bobbinand immersed in acetone at room temperature for one minute. This yarnwas then skeined and hung in boiling water, tension free, for oneminute. Crimp developed readily. Crimp retentivity was found to behigher tl1an 90% when measured according to the new method describedabove. Miscroscopic inspection of the crimped filaments showed that thecrimp was the beta type.

In the foregoing examples the filaments were spun through the spinneretshown in Figure 2 which was found to be especially suited and economicalto be used for obtaining a random eccentric sheath-core structure in thesingle filaments. However, the invention is not limited to theapplication of this specific spinneret. Any other form of a spinneretwhich permits production of a composite filament which contains at leasttwo components in an eccentric relationship over the full length of thefilament can be used. There are no restrictions with respect to whichcomponent forms the core and which component forms the sheath in thesheath-core structures of this invention. Though it is generallypreferred to choose the component with the higher tensile recoveryproperties to form the sheath, other considerations like solubility,spinning technique, appearance and hand, and physical properties maymake the reverse order desirable. The invention is further not limitedto the eccentric sheath-core filaments. Any other form of a compositefilament which contains the components in an eccentric relationship overthe cross-section of the single filament may be utilized instead of thesheath-core structure shown in the examples. So for instance, thecomponents can also be spun in the so-called side-by-side relationshipwherein the components are combined at only part of their surface andboth components take part of the surface of the composite filament.However, the sheathcore structures are preferred in this inventionbecause the problem of coherence, which exists with many polymercombinations, particularly on drawing the sideby-side structures, inpractically eliminated in sheathcore structures. The latter structurestherefore permit a much wider application of this principle. Otherembodiments include composite filaments which are composed of more thantwo components. Flaments have been produced in the above examples whichconsist of about equal parts of the two components. However, sometimesit might be preferred to use a relatively higher amount of one componentand a correspondingly lower amount of the other component. Good resultscan usually be obtained with compositions of at least 20% by weight ofone component and 80% by weight of the counterpart up to a ratio of 50%by weight of both components. Those composite filaments containing aboutequal portions of both components are preferred because of the highertightness and permanence of the crimp achieved.

' Sometimes it might be desirable to spin a bundle of filaments whichcomprises composite filaments containing the components in variousratios through one and the same spinneret. An example is a bundle oftwo-component composite filaments which comprises filaments consistingof 20% by weight of the load-bearing component and 80% by weight of theother, a 30% /70% ratio, a 40% /60% ratio and a 50% /50% ratio,respectively. Such filament bundles containing composite filaments withvarious ratios of components can very convenientlvbe produced byutilizing the spinneret which is shown in Figures 6 and 7. The spinneretshown is composed of two parts. In the upper portion 16 are two chambers17 and 18 cooperating with holes 19 in the bottom plate of the topportion. These holes permit the feeding of polymer to grooves orrecesses 20 in the bottom portion 21 of the spinneret. The polymercoming from hole 19 goes into the recess 22 immediately below it and isfed to a plurality of recesses 20. Each recess contains and cooperateswith a spinneret hole 24. In each spinneret, provision is made for agasket 25 and conventional means, as by bolting or pressure, can be usedto hold the various spinneret elements in place during operation.

However, in the spinneret shown by Figures 6 and 7 there is no tubelocated in the spinneret orifices 24 such as are in the spinneretorifices 9. Thus, in this modification polymer coming from chamber 17and the other polymer coming from chamber 18 meet at the orifices 24 andare extruded simultaneously to form side-by-side structures.Cross-sections of such structures are shown in Figure 9, thesestructures being designated by reference number 26, the parts being 27and 28.

The spinning, drawing, and length stabilization of the load-bearingcomponent in the composite filament and the after-treatment for bringingabout the crimp were described in the foregoing as a discontinuousprocedure wherein each treatment was carried out as a separateprocessing step. The same outstanding results however can be achieved ina fully continuuous process. An apparatus especially useful for thecontinuous procedure is shown in the schematic drawing of Figure =12.

The apparatus comprises a draw pin 32 at which the stretching ocurs, aheating medium 33 such as a hot metallic surface, and a draw roll 34.The following Example V is representative of a continuous process forproducing the composite filaments having the reversed permanent betacrimp.

Example V Following the procedure described in Example I, compositesheath-core poly(ethylene terephthalate)- poly(hexamethylene adipamide)filaments are extruded through a spinneret like that shown in Figure 2having 34 holes. The filaments 35 are attenuated by drawing them fromthe spiuneret at approximately 500 times the speed with which thepolymer leaves the spinneret holes. The bundle of filaments is, aftercooling, continually drawn over a draw pin 32 which is heated to C. Onits path to the draw roll the filament bundle is led over a hot plate 33which is heated to C. The total draw imposed on the yarn is 3.56. Thefilaments, the thickness of which corresponds to approximately 2deniers, are substantially uncrimped but they possess the potentialcrimp. Subsequent tensionless treatment in boiling water by shortimmersion developed readily a tight helical crimp. The crimped filamentshave on an average approximately 60 crimps per inch and a crimpelongation of and a crimp retention of 90% when measured according tothe above-described test with the application of a load of 1 g./denierfor 30 seconds. Microscopic inspection of the crimped filaments showedthat the filaments have the beta-type crimp wherein the thicker portionsof the polyamide skin form the inside of the single coils.

Similar composite filaments produced according to the foregoing methodhowever omitting the length stabilization on the hot plate had a crimpelongation of only 70% and a crimp retention of only 40% when measuredby the test used above.

Suitable components for producing the permanently crimpable compositefibers by the process which includes the length stabilizing step can befound in all groups of synthetic fiber-forming materials. Because oftheir commercial availability, ease of processing and excellentproperties, the condensation polymers, e.g., polyamides,polysulfonamides and polyesters and particularly those which can readilybe melt spun are preferred for application in this method. Suitablepolymers can be found for instance among the fiber-forming polyamidesand polyesters which are described e.g. in US. 2,071,250, US. 2,071,253,US. 2,130,523, 2,465,319, US. 2,130,948, US. 2,190,770 and in otherplaces. A preferred group of polyamides comprises such polymers aspoly(hexa methylene adipamide), poly(hexamethylene sebacamide),poly(epsilon-caproamide) and the copolymers thereof. Among thepolyesters may be mentioned, besides poly- (ethylene terephthalate),which is preferred for most applications, the corresponding copolymerscontaining small amounts of sebacic acid or adipic acid as well as thepolyesters containing recurring units derived from glycols with morethan two carbons in the chain.

Fiber-forming polysulfonamides can be produced by reacting at aninterface between two immiscible phases organic sulfonic acid halides,e.g. dichlorides, which form or are contained in one phase, with primaryor secondary organic diamines which form or are contained in the otherphase, whereby preferably one of the phases is dispersed in the otherwhile the reaction takes place. Such a method is described, forinstance, in US. Patent 2,667,468.

Another group of condensation polymers which can be used in thisinvention, comprises the polymers which contain sulfonamide groups aswell as carbonamide groups. These polymers are conveniently produced bythe same method as described above, however, substituting the disulfonicacid halides by the corresponding organic monocarboxylic, sulfonic aciddihalides.

The above-described interfacial polymerization methods may also be usedfor producing the polyamides, when organic dicarboxylic acid halides areused instead of the sulfonic acid halides. When diearboxylic acidhalides are reacted with glycols in the above reactions, thefiberforming polyesters are obtained. Other groups of polymers useful ascomponents in the filaments of the present invention can be found amongthe polyurethanes or polyureas which may be made either by conventionalmethods or by theabove-described interfacial methods as well as amongthe polyvinyl compounds including such polymers as polyethylene,polyacrylonitrile, polyvinyl chloride, polyvinylidene chloride, andsimilar polymers.

9 It is evident from the foregoing description that the compounds areoperative inthe method comprising the length stabilization step onlywhen the materials are combined in the composite filaments in such a waythat the normally load-bearing component which is the component with thehigher shrinkage can be length stabilized under conditions which do notsubstantially reduce the residual shrinkage of the other component sothat a differential in shrinkage of at least and preferably or more isachieved Actually, after the length stabilizing treatment, the normallyload-bearing component has a lower shrinkage than the other componentand reversal of crimp results. The physical properties and particularlythose properties as residual shrinkage,

tensile recovery, or permanent set by extension among others of thefiber-forming polymers are well known and can easily be determined.Therefore, by comparing the physical property data of the desiredcomponents, the operability of any given combination according to thepresent invention can easily be determined by following the teachingsgiven herein.

The fiber-forming high polymeric materials can be length stabilized bycrystallizing the polymer under conditions wherein no shrinkage canoccur. In other words the crystallization is efiected under conditionsof tension which equals the forces developed in the filaments during thetreatment. respectively of many of the fiber-forming high polymericmaterials can therefore be accomplished preferably by a heat treatmentof the taut filaments. This is usually applied when the normallyload-bearing componentin Example I this is the poly(ethyleneterephthalate)- has the lower apparent minimum crystallizationtemperature (T T for poly(ethylene terephthalate) is 99 C. Thetemperature applied should generally be higher than the apparent minimumcrystallization temperature of the normally load-bearing component whichis well known or can easily be determined for each polymer. A convenientmethod for determining the apparent minimum crystallization temperature(T,) is described e.g. in US. 2,578,899. In order to achieve the resultsof the present invention, namely, length stabilizing one component andnot aifecting to a substantial extent the residual shrinkage of theother component, a temperature is preferably chosen which is lower thanthe apparent minimum crystallization temperature of the counterpart.However, depending on the nature of the other component or components inthe combination and the length of time of exposing the compositefilaments to the taut heat treatment, a higher or lower temperature canbe chosen to achieve optimum results and the tightest possible crimp.The temperatre range for the taut heat treatment may vary in wide limitsand may be up to about 100 C. or more above T, of the normallyload-bearing component. Usually, however, best results are obtained whenapplying a temperature in the range of 5 C. to 70 C. above T, of thenormally load-bearing component. The lower temperatures in this rangeare applied when the composite filaments are exposed to the taut heattreatment for longer periods of time, e.g. for 30 to 60 minutes, whilethe higher temperature range is applied with shorter heat treatments,e.g. of some minutes or seconds or less. The temperature of the heattreatment should in any event, however, be lower than the softening ormelting temperature of the lower melting component in the compositefilament. For a given combination with a given set of processingconditions, however, the temperature of the taut heat treatment is verycritical and usually should be kept in a range of plus or minus 10 toplus or minus of its optimum temperature in order to achieve maximumresults. In the continuous process shown in Example V the temperature of140 C. at the hot plate should be maintained within the limits ofapproximately plus or minus 10 C. in order to produce a yarn withmaximum crimp retention and crimp tight- Crystallization or lengthstabilizationlength stabilization,

l0 ness. If optimum properties are not desired, the temperature of thehot plate could be varied in limits of about plus or minus 15 to 20 C.Even though the temperature of the draw pin is not as critical as thetemperature of the hot plate, it should not vary more than approximately30 C. and preferably 15 C. from the temperature of C. used in theforegoing example. As already pointed out with varying spinning andprocessing conditions and with dilferent combinations of materials, theoptimum temperatures may vary in wide limits.

It is known that not only elevated temperatures bring aboutcrystallization and length stabilization of a given polymer but alsoother special conditions under which the material is treated. Thus, forinstance, the presence of plasticizers has a great effect on thetemperautres necessary to achieve crystallization and reduction ofresidual shrinkage. This can be utilized in the present invention byadding a plasticizer to the normally loadbearing" component. This can bean organic plasticizer as commonlyused in polymer applications which maybe subsequently removed. Water may take the function of a plasticizerespecially when the two polymers differ in their ability to absorbmoisture.

On the other hand, for instance, when poly(hexamethylene adipamide) andpoly(ethylene terephthalate) are used in a combination wherein thepolyamide forms at least part of the outer skin of the compositefilament, it is advantageous to remove most of the moisture from thepolyamide before or while applying the taut heating step of thisinvention. The reverse situation may be true with other combinations. Byvarying these conditions, as well as the lengths of time of the heattreatment and/or the temperature of the treatment, the tightness ofcrimp and crimp permanence can be varied. In order to obtain a crimp astight as possible, optimum conditions for the stabilizing treatment aregenerally observed.

With some combinations of high polymeric materials it is not possible toavoid fully the reduction of residual shrinkage of the co-actingcompound or compounds in the composite filaments when the lengthstabilization is brought about by heating to a temperature higher thanthe apparent minimum crystallization temperature of the normallyload-bearing component. This is true, for instance, when the normallyload-bearing component has a higher apparent crystallization temperaturethan its counterpart. In these instances and also for other reasons,sometimes other methods might be preferred for crystallizing or lengthstabilizing the normally loadbearing component. A very convenient methodcomprises the exposure of the composite filament, while in tautcondition, to the action of certain polar organic liquids which arelatent solvents for the amorphous regions of the load-bearing componentand which therefore promote crystallization of the normally load-bearingcomponent but do not affect the other component or componentssubstantially. A suitable liquid will be chosen depending on thespecific combination of polymeric materials. In a combination ofpolyethylene and poly- (ethylene terephthalate), for instance, acetonehas proven to be an excellent material to promote crystallization of thepoly(ethylene terephthalate). Other suitable polar liquids are, forinstance, chloroform, methylene chloride, tetrachloroethane, phenol,m-cresol among others. In those liquids having too great swellingaction, dilution with water or other less active liquids may benecessary. Temperatures and other conditions of .the liquid treatmentmay be varied in wide limits with various combinations of polymers toachieve every desired result with respect to the tightness, permanenceand appearance of the beta crimped filaments. Example IV above shows thepreparation of a composite filament from polyethylene and poly(ethyleneterephthalate), using a liquid treatment for length stabilization.

In addition to the methods described above involving there is anothermethod for producing the new composite crimped filaments of thisinvention. This method does not require the length stabilizing step.This method comprises spinning'together two or more synthetic polymericfiber-forming materials, of which the material having the highershrinkage after drawing also has the higher tensile recovery properties.The spinning is done as before so that the materials form over thecross-section of the single composite filament two or more distinctzones which extend through the entire length of the filament ineccentric fashion, whereby only one or part of, or all the componentstake part in forming the surface of the single filament, stretching thecomposite filament, and subjecting the drawn'composite filaments, insubstantially tensionlessstate to a shrinking treatment. In this method,synthetic high polymers forming the load-bearing component should have aresidual shrinkage of at least and preferably more than 15% afterdrawing them at least to twice the original length and a tensilerecovery of at least 90% at 50% of the elongation-at-break combined witha high extensibility, corresponding to at least 10% and preferablyelongation-at-break. Depending on the shrinkage characteristics of theco-acting component, even higher limits of these values may be necessaryto produce a differential in shrinkage between the two materials of atleast 10%.

Synthetic, fiber-forming polymeric materials having the high tensileresidual shrinkage and high recovery properties combined with the highextensibility required by this process, which does not require thelength stabilization step, are generally not found among the polymerscommonly used for producing fibers. However, a limited number of newerpolymers which are produced at preferably moderate temperatures, e.g.according to the abovernentioned interfacial polymerization methods,fulfil these requirements in an ideal way. Such polymers are describedfor instance in copending patent applications Serial No. 345,728, filedMarch 30, 1953, now Patent No. 2,7 31,446 to Wittbecker and Serial No.359,975, filed June 5, 1953, and now abandoned. As co-acting componentscan be chosen any fiber-forming synthetic polymer-which can be spun withthe load-bearing component and which has a residual shrinkage at least5% and preferably 10% lower than the load-bearing component. Thesephysical properties can easily be determined by the commonly used andgenerally known testing metheds.

The conditions applied for drawing the spun multicomponent filaments ofthis invention may vary in wide limits. Instead of using a pin asmentionned in Example I, other convenient means for drawing thefilaments may be applied, for instance, rolls being driven at differentspeeds. Also, the temperatures at which the filaments 'are drawn mayvary in wide limits and depend mostly upon the properties of the singlematerials forming the composite filament and of the final desiredresults. As is the case in the production of conventional unitaryfilaments, the preferred drawing temperatures for the compositefilaments of this invention may vary between room temperature orslightly elevated temperatures and temperatures of about 100 C. up torelatively high tem peratures which may in some cases be as high asabout 70 C. below the melting point of the lower melting material. Sincein the present invention combinations of at least two differentmaterials are employed, the specific drawing characteristic of eachmaterial used should be considered in order to obtain best results. Ingeneral, it is of advantage to use drawing temperatures which are lowerthan the apparent minimum crystallization temperature (T of the normallyload-bearing component. This latter limitation of the drawingtemperature rnay become of particular importance in the method whichemploys the length stabilization step.

The composite filaments have been produced in the examples by the meltspinning technique. Naturally,

also any other spinning method like plasticized melt spinning, dryspinning, wet spinning, can be employed successfully. In some instances,particularly when the melting behavior or the solubility of thecomponents in a combination would not permit spinning the compo nents bysimilar methods, a combination of dissimilar methods is indicated. Thus,for instance, one component, preferably the component forming the sheathcan be spun as a solution in a high boiling solvent or as a plasticizedmelt, while the core-forming component is extruded as the moltenpolymer. Similar combinations of spinning methods can be used forspinning side-by-side structures. In these instances, the solvents orplasticizers may be wholly or partially removed subsequently, preferablyby washing them out by the help of low boiling solvents.

In the method involving length stabilization, as shown in Example I, thecomposite filaments are substantially uncrimped after the application ofthe length stabilization treatment but contain, however, a potentialcrimp. The crimp can be developed in these filaments very readily by asuitable after-treatment. The filaments containing the potential crimpcan be processed as any ordinary uncrimped continuous filaments orstaple fibers to worsted or knitted goods. The crimp can then be imposedon the filaments at any time by a suitable relaxing orshrinkagetreatment. This shrinkage treatment was performed in theforegoing examples by exposing the composite filament containing thepotential crimp to boiling or hot water. Good results, however, may alsobe obtained, for instance, by the application of moist heat or steam.Which of these after-treatments for bringing about the crimp are chosendepends mostly on the properties of the components forming the compositefilaments and on the final properties which are desired in the crimpedfilaments. In general, the temperature applied in the crimping procedureshould be higher than the apparent second-order transition temperatures(T of the polymers forming the composite filament in order to achievethe favorable results of the invention. The apparent second-ordertransition temperature (T of a polymer is defined as the temperature atwhich a discontinuity occurs in the curve of a first derivativethermodynamic quantity with temperature. A convenient method formeasuring this temperature is shown in U.S. Patent No. 2,578,899. Sincewater acts as a plasticizer in many polymers, thus lowering the apparentsecond-order transition temperature (T this should also be considered inmeasuring T and in selecting the appropriate crimping method andtemperature. Other factors influencing the optimum condition forcrimping the composite filaments of this invention are, for instance,the spinning, drawing and length stabilizing conditions used and alsoother factors, for instance, whether the composite filament is processedas continuous filament or as staple or as a woven or knitted textilefabric. Therefore, by varying the after-treating conditions for bringingabout the crimp, also the properties and appearance of the cr-impedfilaments can be varied to a great extent in any desired way.

In summary, polymers which are useful as the loadbearing component inthe fibers of this invention to produce useful textile materials may bedetermined by subjecting a filament from the polymer to the processingsteps of this invention in the absence of other components and testingcertain properties of the resultant filament. Such a filament shouldhave (1) a minimum initial modulus of at least 5.0 grams per denier, (2)a shrinkage of at least 7%, (3) a permanent set at an extension thatcorresponds to 50% of its elongation-at-break of below 10% and (4) theelongation-at-break shouldbe higher than 15%.

In general,.the composite filaments are drawn from about 2 times toabout 8 times their original lengths. Prior to drawing the filaments areattenuated; that is, they are slenderized by pulling the freshlyextruded filaments away from the orifice at a rate faster than theextrusion rate. The drawing or orientation step is in addition toattenuation, but also has a slenderizing effect. The extent of drawingwill, of course, also depend somewhat upon the nature of the particularpolymers used in the composite filament and upon the type of eccentricrelationship between those polymers in the composite filament.

In the hot relaxing treatment of this invention used to develop thepotential crimp, the medium may be any inert atmosphere capable of beingheated to a temperature of about 100 C. Thus, the filaments may beheated in air, nitrogen, hot or boiling water, carbon dioxide or anygaseous or liquid media inert to the polymers in the compositefilaments. The temperature used is generally in the neighborhood of 100C., but it may be lower or higher. For example, any temperature aboveabout 50 C., but below the melting point of the lowest melting polymericconstituent in the composite fiber, may be used. Generally, atemperature in the range of about 50 C. to about 150 C. is used with convenience.

The length of time that the composite filaments are subjected to thehot, relaxing treatment is not critical, because the crimp developsimmediately and spontaneously. Thus, the time may be very short, as, forexample, a matter of seconds, although it may be desired in some casesto continue the length of treatment for a longer period of time such as30 minutes, or even for several hours.

Further, the spinnerets described herein may be simplified in certainrespects. To illustrate, the tube 31 in the spinneret shown in Figure 2may be dispensed with, for hole 8 in the adapter is eccentricallylocated above and in respect to orifice 9, and the jetting of polymer 13into the melt of polymer 14 and the polymer flow thereafter leads to asheath-core structure. Also, the provision of recesses 23 of relativelylarge area in conjunction with channels 6 of smaller area, as shown inthe spinneret assembly given in Figure 2, results in the formation ofridges between the channels. These ridges can be removed both in theadapter or spinneret plate. That is, one very large recess is provided,the orifices being appropriately placed, and the polymer fed underpressure flows to the various orifices.

The crimped two-component filaments of this invention show a tightpermanent crimp. The crimp obtainable in this invention correspondsusually to more than crimps per inch and up to 300 crimps per inch. Thecrimp permanence is 50% up to 100% when measured and calculated by thetest described above, and those composite filaments having a crimppermanence of about 80% or more are preferred.

It is well known that, in many applications of the continuous orstaple-length crimped filaments in textile materials, sometimesrelatively high tensions are applied to the fabrics and thus to thesingle filaments in daily use of these materials. Therefore, high crimpretention, also under high tensions, which is necessary for dimensionalstability of the worsted or knitted goods from these crimped filamentsis very important for practical application of the crimped filaments.

The characteristic of the new crimped filaments containing the betacrimp to retain the original high crimp also after the application ofhigh tensions or high loads to the filaments makes them especiallyuseful for many textile applications where bulky highly crimpedfilaments are desired and where high crimp retention under high stressis of great importance. This applies also to the crimped filaments whichare cut to staple length and which are usually spun into yarns andprocessed according to known textile processing methods to knitted orwoven goods. The new staple filaments of this invention can be crimpedbefore they are further processed or in any state of processing, forinstance, after they are spun into yarns or after the woven or knittedgoods are made from these yarns. Another important application comprisesthe processing of the continuous filaments into bulky fabrics whichagain can be carried out vw'th the continuous filaments in the crimpedor uncrimped state. In the latter case, the crimp can be developed afterweaving or knitting the yarns obtained therefrom or in any stage of theprocessing. Very interesting applications of the continuous yarns are,for instance, the preparation of worsted fabrics which may be woven fromthe uncrimped yarns containing the potential crimp and which are crimpedafter weaving and finishing. These worsted fabrics have an appearanceand hand very similar to those obtained from staple yarns. However, theydo not possess the disadvantages in processing and use of these fabrics.Another very important application of the fibers of this inventioncomprises the use in carpets and other heavy textile goods where againthe fibers containing the potential crimp can be knitted or woven andthe crimp is developed in the finished goods.

Any departure from the above description which conforms to the presentinvention is intended tobe included within the scope of the claims.

I claim:

1. A helically crimped filament comprising at least two different,synthetic polymers one of which constitutes the load-bearing componentin said filament, the said polymers having different recovery propertiesand being contained in said filament as substantially separatecomponents held together in eccentric relation to each other, theload-bearing polymeric component of said filament being located at theinner portion of the helical coils and being the polymer having thebetter tensile recovery properties.

2. A filament in accordance with claim 1 wherein said relation is asheath-core relation.

3. A filament in accordance with claim 1 wherein said relation is aside-by-side relation.

4. A filament in accordance with claim 1 wherein one of said polymers isa polyamide.

5. A filament in accordance with claim 1 wherein one of said polymers isa polyester.

6. A filament in accordance with claim 1 wherein one of. the saidpolymers is a poly(ethylene terephthalate).

7. A filament in accordance with claim 2 wherein the load-bearingcomponent is a polyamide and said polyamide constitutes the sheath.

8. A helically crimped filament made from at least two syntheticpolymers differing in recovery properties, one of which polymers beingthe load-bearing constituent in said filament, said filament comprisinga polyamide and a polyester having different recovery properties andcontained in said filament as substantially separate components heldtogether in eccentric relation to each other, the said polyamide beingthe load-bearing constituent appearing at the inner portion of thehelical coil and being the polymer having the better tensile recoveryproperties.

9. A filament possessing potential crimp comprising at least twodifferent, synthetic polymers one of which constitutes the load-bearingcomponent in said filament, the said polymers having different recoveryproperties and being contained in said filament as substantiallyseparate components held together in eccentric relation to each other,said filament being capable of developing a permanent helical crimpwherein the load-bearing component appears at the inner portion of thehelical coil and has the better tensile recovery properties.

Graves Apr. 15, 1941 Kulp et al. Oct. 2, 1945 (Other references onfollowing page) UNITED STATES PATENTS Sisson Sept. 30, 1947 Kulp et a1.1 Apr. 20, 1948 Sisson Apr. 20, 1948 Sisson Apr. 20, 1948 Sisson et a1.May 4, 1948 Ladisch Oct. 7, 1952 16 Ladisch Apr. 6, 1954 Latour Aug.23,1955 Boeuf Mar. 6, 1956 FOREIGN PATENTS Grat Britain Nov. 14, 1939

1. A HELICALLY CRIMPED FILAMENT COMPRISING AT LEAST TWO DIFFERENT,SYNTHETIC POLYMERS ONE OF WHICH CONSTITUTES THE LOAD-BEARING COMPONENTIN SAID FILAMENT, THE SAID POLYMERS HAVING DIFFERENT RECOVERY PROPERTIESAND BEING CONTAINED IN SAID FILAMENT AS SUBSTANTIALLY SEPARETECOMPONENTS HELD TOGETHER IN ECCENTRIC RELATION TO EACH OTHER, THELOAD-BEARING POLYMERIC COMPONENT OF SAID FILAMENT BEING LOCATED AT THEINNER PORTION OF THE HELICAL COILS AND BEING THE POLYMER HAVING THEBETTER TENSILE RECOVERY PROPERTIES.